Such flap devices serve, for example, as exhaust gas retention flaps or exhaust gas recirculation flaps in the exhaust system of an internal combustion engine. Exhaust gas contains pollutants that must be prevented from escaping to the outside so that a reliable sealing must be ensured along the shaft which extends outward towards an actuator. This sealing must function perfectly at all times under varying thermal loads. A very precise controllability must also be observed with the flaps in order to meet pollution emission standards for modern internal combustion engines. It has been found, however, that damage at the bearing site is caused even more often by ingress from outside. This leads to corrosion in the area of the bearing, caused by the introduction of dirt or by the introduction of salt and humidity.
Various flap devices have previously been described which have attempted to ensure a sufficient sealing. WO 2006/003017 A1, for example, describes a flap valve for an exhaust system of a motor vehicle, wherein a bearing bush, as well as a spring element, a sealing disc, and a bearing ring, are arranged in a bearing housing fastened to the flow housing. The shaft protrudes out from the bearing housing which has a conical restriction at its end facing away from the flow housing and surrounding the opening through which the shaft protrudes, the spring force pressing the correspondingly conical surface of the bearing ring against the restriction with interposition of the sealing disc. The contact area of the conical surfaces serves as a sliding and sealing surface between the bearing housing and the bearing ring. An escape from the bearing region along the shaft is intended to be achieved by placing the sealing disc in a manner free of play.
An exhaust gas flap is also described in U.S. Pat. No. 5,630,571, the exhaust gas flap comprising a bearing housing in which a bearing bush and a spherical sealing disc are arranged, which disc is in contact with a negative spherically shaped ceramic disc. The end of the shaft protruding from the bearing housing is provided with a lever against the rear side of which a wave spring rests, the opposite side thereof being in contact with a bush which is, in turn, in contact with the ceramic disc. The sealing disc pressed on the shaft is urged against the stationary ceramic disc by the wave spring. The outer bush is, however, thereby subjected to exposure to spray water in the internal combustion engine.
The components in each of these two above-described exhaust gas flap sealing systems must be manufactured with an extremely high precision in order to provide sufficient sealing since the correspondingly shaped surfaces would otherwise have no sealing effect. An ingress of corrosive substances into the bearing region from outside cannot therefore be prevented in a reliable manner. A great number of components is moreover required, which results in an increased assembly effort.